The overall goals of the proposed research are to investigate the development of sustained attention in infants and preschool children, to assess the extent to which there are stable individual differences, and to develop measures of attention that will be of use in both basic and clinical research. In addition to a currently funded longitudinal study of attention and impulse control, four projects are proposed. Two concern different types of sustained attention: 1) attention maintained for the purpose of acquiring information or solving a problem; and 2) attention maintained in anticipation of an event about to occur, that is, vigilance. These two projects involve infants and preschoolers, respectively, but both deal with the relationship of the two kinds of attention to each other, their resistance to distraction, and the issue of individual differences and continuity. Both of these projects build on previous work, but also require the development of new procedures for studying attention. Specifically, these new procedures include an analogue of vigilance tasks, now used with older children, for use with infants in the second half of the first year, and a downward extension of the continuous performance test for use with children as young as two years. The other two projects are clinical investigations that use measures of attention as outcome variables. One is a study of the effects of treatment on brain function and behavior in moderately lead intoxicated children; the other is a study of the consequences of neonatal brain dysfunction on specific aspects of cognitive development. All of the proposed studies should lead to theoretical advances in our understanding of attentional control and to clinically useful techniques for the study of early deviations in attention.